From 3b2aa8f209fb50f62935044358651db0ea176c91 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 9 Oct 2017 12:40:00 -0700 Subject: [PATCH] FS-Cache: fix dereference of NULL user_key_payload commit d124b2c53c7bee6569d2a2d0b18b4a1afde00134 upstream. When the file /proc/fs/fscache/objects (available with CONFIG_FSCACHE_OBJECT_LIST=y) is opened, we request a user key with description "fscache:objlist", then access its payload. However, a revoked key has a NULL payload, and we failed to check for this. request_key() *does* skip revoked keys, but there is still a window where the key can be revoked before we access its payload. Fix it by checking for a NULL payload, treating it like a key which was already revoked at the time it was requested. Fixes: 4fbf4291aa15 ("FS-Cache: Allow the current state of all objects to be dumped") Reviewed-by: James Morris Signed-off-by: Eric Biggers Signed-off-by: David Howells [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- fs/fscache/object-list.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c index ebe29c581380..53d7fd3c6344 100644 --- a/fs/fscache/object-list.c +++ b/fs/fscache/object-list.c @@ -338,6 +338,13 @@ static void fscache_objlist_config(struct fscache_objlist_data *data) rcu_read_lock(); confkey = key->payload.data; + if (!confkey) { + /* key was revoked */ + rcu_read_unlock(); + key_put(key); + goto no_config; + } + buf = confkey->data; for (len = confkey->datalen - 1; len >= 0; len--) { -- 2.39.2